substance: WO3
property: defects
For WO3–x electron microscopy, density and XRD have established that for x ≤ 10–4 point defects, primarily
oxygen vacancies, predominate, whereas for x ≥ 10–4 crystalline shear planes oriented in the {10m} directions
of the ReO3 phase are found. The oxygen deficit is accompanied by a marked colour change from yellow to
green and finally to black. EPR data of slightly substoichiometric WO3 after IR illumination showed a signal
ascribed to W5+ [77G]. The change in resistivity with oxygen pressure at 750 oC is shown in Fig. 1 and there is
clear evidence for seven shear-like phases [77G].
References:
77G
Grazzinelli, R., Schirmer, O. F.: J. Phys. C 10 (1977) L145.
Fig. 1.
WO3–x. Resistivity vs. oxygen partial pressure at 750oC for both single crystal (left hand scale) and sintered
discs. Values of x in the range 0...0.04 [77G]. Orientation for single crystals not specified.